First of all I apologize about the subject heading but I just couldn't help myself.

Now for the issue at hand - has there been any studies that directly correlates HR to Lactic Acid Production, or do we just indicate that Lactic Acid Production usually takes place at a specific heart rate or HR range. I hope that does not sound too confusing. Let me know if this question needs further explaining on my part.

Next, if Lactic Acid Production is independent of HR does this mean that your Heart rate could be elevated due to the release of adrenaline (epinephrine) into the blood and that in turn you could get a high HR reading without producing Lactic Acid?

Doc, if you find any studies on this please paste a link or paste the relevant portion into the forum.

I will take a shot at clarifying the relationship between HR and lactic acid production. To really understand it, you do have to delve into the physiology jargaon, but I will try to translate and simplify as best as possible.

The first thing to understand is that anytime you exercise, you are producing lactic acid. It is a product of the process to turn carbohydrate into energy. At lower intensities, the lactic acid is taken into the mitochondria of the muscle cell, broken down further, and used to produce substantially more energy. At high intensities (above Lactate Threshold), lactic acid is produced more rapidly than it can be absorbed into the mitochondria, so it accumulates in the muscle, causing the all familiar burn.

Now as far as how this relates to heart rate. As your workload (power output) increases, all of the physiological indicators increase. The ones that are usually measured include heart rate, lactic acid production (accumulation in blood), power output, oxygen consumption (VO2), ventilatory rate, and other more technical measures. In a controlled environment all of these indicators increase proportionately to each other. As one (power output) increases they all increase.

So when you go for performance/VO2 testing, they measure all of these things and identify your lactate threshold (LT) or workload at which lactic acid accumulates faster than it can be absorbed into the mitochondria. Once the threshold is identified, they simply look at your other values at that point to define your LT Heart Rate, Power at LT, VO2 at Threshold, etc.

Notice above that I specified this clean process exists in a controlled environment. Other factors can effect these indicators, specially heart rate. The usual culprits are nerves, adrenalin, fatigue, high air tempertaures, illness.

That is greatly simplified, but as clear as I can word it without going into the dark world of exercise phys. jargon.

Adrenaline and other hormones will increase your HR, but not your lactic acid production/accumulation. The only thing that will cause you to accumulate more lactic acid is an increase in your actual workload.

If you ride at a certain workload in a non-competition workout, and the same workload in a race, your heart rate in the race will tend to be slightly higher, due to adrenaline, anxiety, and the other factors unique to race day.

An interesting note on this subject: When you train, one of the changes you bring about over time is an increase in the number of mitochondria in the muscle cells. The more mitochondria you have the more lactic acid you can absorb and the more energy you can produce. So this effect of training lets you more efficiently use carbohydrate and allows you to delay the accumulation of lactic acid and the burn that goes along with it.